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Derivatives - Schedule of Changes in Fair Value of Derivative Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
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Mar. 31, 2013 | Mar. 31, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract] |  |
Increase in other income | $ 989 | $ 606

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- Definition Change in the fair value of derivative assets and derivative liabilities attributable to credit risk included in other income. + References No definition available. + Details
Name: | fcf_ChangeInOtherIncomeDueToCreditRiskOnInterestRateSwaps
Namespace Prefix: | fcf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration